under the application of relatively weak magnetic fields point toward their application as quantum sensors at room temperature. [17,18] Their fabrication flexibility and industrial use in commercial displays [19] underlie recent advances toward the miniaturization and integration of quantum technologies based on these materials. [20][21][22] For effective integration or miniaturization, reproducibility is crucial, and this extends to those properties of materials which impact spin-dependent processes. In this work, we aim to measure the variation of a critical spin property common to organic materials, the Overhauser field, which arises from the hyperfine coupling of charge-carrier spins to the bath of randomly oriented nuclear spins in the molecular environment. [23] The Overhauser field underlies a range of phenomena observed in organic devices, including magnetoresistive and magnetic resonant effects in organic light-emitting diodes (OLEDs), [24][25][26][27][28] both of which have been proposed as a mechanism to enable magnetic field sensing. [17,26] To date, the Overhauser field has been treated as a bulk property of the device, characterized by a single value that describes its impact. [26,29] If this is not a good assumption, it will present a significant challenge as we move toward high spatial resolution of magnetic fields [30,31] in organic devices. [32,33] We will demonstrate in the following sections that the Overhauser field indeed shows substantial intra-device variation by spatially resolving the magnetoluminescence effect exhibited by both a copolymer Super Yellow poly(phenylene-vinylene) (SY-PPV) and a small-molecule tris-(8-hydroxyquinoline) aluminum (Alq 3 ) OLED. As the Overhauser field is central to a wide range of spin-enabled functionality in organic devices, this variation presents a fundamental challenge for efforts to miniaturize and integrate such devices. Concept Magneto-Electroluminescence in OLEDsWe employ a stable and widely investigated active material-SY-PPV-to characterize the spatial variation of the Overhauser field in a simple vertical structure OLED (Figure 1a) and extract Devices that exploit the quantum properties of materials are widespread, with quantum information processors and quantum sensors showing significant progress. Organic materials offer interesting opportunities for quantum technologies owing to their engineerable spin properties, with spintronic operation and spin resonance magnetic-field sensing demonstrated in research grade devices, as well as proven compatibility with large-scale fabrication techniques. Yet several important challenges remain as moving toward scaling these proof-of-principle quantum devices to larger integrated logic systems or spatially smaller sensing elements, particularly those associated with the variation of quantum properties both within and between devices. Here, spatially resolved magnetoluminescence is used to provide the first 2D map of a hyperfine spin property-the Overhauser field-in traditional organic light-emitting diodes (...

Quantum sensing and imaging of magnetic fields has attracted broad interests due to its potential for high sensitivity and spatial resolution. Common systems used for quantum sensing require either optical excitation (e.g., nitrogen-vacancy centres in diamond, atomic vapor magnetometers), or cryogenic temperatures (e.g., SQUIDs, superconducting qubits), which pose challenges for chip-scale integration and commercial scalability. Here, we demonstrate an integrated organic light emitting diode (OLED) based solid-state sensor for magnetic field imaging, which employs spatially resolved magnetic resonance to provide a robust mapping of magnetic fields. By considering the monolithic OLED as an array of individual virtual sensors, we achieve sub-micron magnetic field mapping with field sensitivity of ~160 µT Hz−1/2 µm−2. Our work demonstrates a chip-scale OLED-based laser free magnetic field sensor and an approach to magnetic field mapping built on a commercially relevant and manufacturable technology.

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